The background of the invention will be discussed in two parts:
1. Field of the Invention
This invention relates to laser apparatus, and more particularly to non contact laser engraving apparatus for producing laser engraved images in organic materials such as wood, plastic and paper.
2. Description of the Prior Art
The use of laser apparatus for producing engraved or carved images in a workpiece, such as wood, paper or the like is fairly common. Such laser apparatus ordinarily employs a carbon dioxide laser or the like with means for focusing the beam to a power density of 30,000 watts/square centimeter, this focused beam being scanned over the workpiece, upon which is typically placed a stencilled template. This template has an image in the form of openings therein. The laser beam is then scanned over the entire area of the template, and in the open areas thereof, the laser beam strikes the workpiece causing vaporization of the surface to reproduce the image of the template on the workpiece. The template is formed of a suitable metal, such as copper or brass. With such metal templates there are certain limitations, one such limitation being the amount of detail which can be formed therein. With stenciling the basic means of forming such templates, where it is desired to form fine lines in the finished image, the structural stability of a fine strand of metal in the template creates a limiting factor. In addition, when fine lines exist in the template, twisting or warping, or bending may occur during handling and use of the template. As a further limitation, since metal is normally employed in the template, as the laser beam is scanned thereover, heat is generated as well as smoke as the exposed portions of the workpiece vaporize. With the occurrence of smoke, condensed smoke darkens the metal surface, causing the template to become absorbent. This, in turn, produces rapid heating and cooling when struck by the laser beam, with this thermal working of the metal ultimately distorting the template so that it has a limited useful life.
Another method sometimes used for laser engraving involves a modulation approach in which the workpiece is scanned with an electrically modulated laser beam, with the beam being turned on and off to provide a point-by-point resolution of the desired image. This approach has an economic drawback due to the complexity of modulation equipment, which corresponds to more expense. In addition, present modulation mechanisms for use with carbon dioxide laser apparatus do not permit a high enough modulation frequency to be achieved for mass production of rapidly scanned items, such as paper products.
Non contact laser engraving apparatus has heretofore been utilized in engraving objects made of wood. One such apparatus is shown and described in U.S. Pat. No. 4,156,124 issued to the inventor entitled "Image Transfer Laser Engraving". In the apparatus of this patent, the laser beam and the optics remain stationary relative to each other while the template and workpiece are moved synchronously.
It is an object of the present invention to provide a new and improved laser apparatus.
It is another object of the present invention to provide a new and improved apparatus and method for laser engraving of products such as wood and paper.
It is still another object of the present invention to provide a new and improved laser apparatus and method for achieving nonstencilled laser engraving at good resolution inexpensively.
It is a further object of the present invention to provide laser engraving apparatus using a cylindrical mirror having a diffusely reflecting artwork image formed thereon or in proximate relation thereto.